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【多选题】
洛杉矶光化学烟雾污染事件中的二次污染物主要是（）。A.
碳氢化合物
B.
氮氧化物
C.
臭氧
D.
过氧乙酰硝酸酯
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【单选题】Nearly half a million immigrants，many of them English—speaking， in the country during the last quarter of the nineteenth century．
A.
have arrived
B.
had arrived
C.
arrived
D.
have been arriving
【单选题】某交流用电器的额定电压为220 V 、额定频率为50 Hz ,其两端加上下列哪种正弦电压,会保证其正常工作______。
A.
220 sin（ 314t +45º ）V
B.
220 sin（ 314t +45º ）V
C.
380 sin（ 314t +45º ）V
D.
220 sin（50 t +45º ）V
【单选题】According to the essay, what role has English played during the process of globalization?
A.
It has created new education opportunities.
B.
It has sped up the process of globalization.
C.
It has opened the doors for new opportunities and increased the number of young women in the working world.
D.
It has increased the number of skilled women.
【单选题】It was during ______ when the English navy defeated the Spanish Armada.
A.
the Middle Ages
B.
the 16th century
C.
the Elizabethan age
D.
the Wars of the Roses
【单选题】某交流用电器的额定电压为220V、额定频率为50Hz,其两端加上下列哪种正弦电压,会保证其正常工作______。
A.
–311sin314tV
B.
220sin314tV
C.
380sin314tV
D.
311sin50tV
【单选题】某交流用电器的额定电压为 220V 、额定频率为 50Hz ,其两端加上下列哪种正弦电压,会保证其工作正常?
A.
u=-220 sin314tV
B.
u=220sin314tV
C.
u=380sin314tV
D.
u=-220 sin50tV
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